Mathematical Modeling of Hollow Fiber Gas-Liquid Membrane Contactors for Acid Gas Removal

The removal of acid gases such as CO₂, SO₂ and H₂S from industrial and natural gases is an important separation process. Membrane gas absorption is a hybrid approach wherein the advantages of both absorption and membrane processes are combined for cost-effective separation and removal of acid gas components from industrial and natural gases.  Gas Technology Institute (GTI) and PoroGen Corporation are jointly developing novel PEEK (Poly-Ether-Ether-Ketone) based gas-liquid membrane contactors for CO₂ and H₂S removal. Extensive laboratory and bench-scale testing with different membrane module sizes are underway at GTI to bring this technology to commercialization. In these membrane contactors, the acid gas stream passes through the tube side of the hollow fiber while a chemically reactive solvent flows through the shell side of the module. The acid gas components permeate through the membrane and are absorbed in the selective solvent by chemisorption. The rich solvent is then thermally regenerated in a second hollow fiber contactor operated in reverse mode and recycled to the absorber module. The coupled mass and heat transport equations reflecting the absorption and desorption processes are formulated and solved both in one-dimensional (1-D) and two-dimensional (2-D) space coordinates. The models use plug and parabolic velocity profiles for the gas flow in the tube side. Velocity profiles for the shell side solvent flow include both plug flow and Happel’s free surface model. The coupled differential equations are solved using an Excel VBA platform combined with process simulators (Aspen Plus® and Aspen HYSYS®) yielding the concentration and temperature profile of the fluid streams. In this scheme, the mathematical calculations are performed in the Excel modules with the process simulators supplying the required fluid properties.